The use of opto-sensors in photographic cameras is well known. They are typically used for such purposes as film metering, setting lens position, reading bar codes, sensing lens parking position, sensing shutter position and the like. When multiple sensors are used in a camera, the outputs of each opto-sensor are connected to a different input terminal of the camera controller (microcomputer). Thus with this arrangement, as shown in FIG. 2, the controller would require as many input pins as there are opto-sensors to be accommodated. It would lower the cost of the controller and simplify operation if the number of input pins were to be reduced.
Ideally, multiple opto-sensors would be provided that uniformly provide output signals that are digital in form (TTL or CMOS). However, due to wide sensor current variations and also due to system tolerance variations caused by such things as differences in reflection or transmission characteristics of the sensed target, distance between sensor and target, tilt, etc., it is difficult to find a single output load impedance value for multiple sensors that would provide adequate and reliable output over the wide range of tolerance variations encountered in actual operation.
It is therefore desirable to provide an opto-sensor input control system for a camera that utilizes a reduced number of input terminals at the camera controller to accommodate multiple opto-sensor inputs. It is further desirable to provide such an input control system that assures that inputs to the camera controller are reliably digital in form irrespective of variations in sensor operation or camera system tolerance variations.